Inducible cyclic AMP early repressor produces reactivation of latent herpes simplex virus type 1 in neurons in vitro

Herpes simplex virus type I (HSV-1) establishes a latent infection in neuro ns of the peripheral nervous system, During latent HSV-1 infection, viral g ene expression is limited to latency-associated transcripts (LAT). HSV-1 re mains latent until an unknown mechanism induces reactivation. The ability o f the latent virus to periodically reactivate and be shed is essential to t he transmission of disease, In vivo, the stimuli that induce reactivation o f latent HSV-I include stress, fever, and UV damage to the skin at the site of initial infection. In vitro, in primary neurons harboring latent HSV-1, nerve growth factor (NGF) deprivation or forskolin treatment induces react ivation. However, the mechanism involved in the induction of reactivation r emains poorly understood. An in vitro neuronal model of HSV-1 latency was u sed to investigate potential mechanisms involved in the induction of reacti vation of latent HSV-1. In situ hybridization analysis of neuronal cultures harboring latent HSV-1 showed a marked, rapid decrease in the percentage o f LAT-positive neurons following induction of reactivation by NGF deprivati on or forskolin treatment. Western blot analysis showed a corresponding inc rease in expression of the cellular transcription factor inducible cyclic A MP early repressor (ICER) during reactivation. In transient-transfection as says, ICER downregulated LAT promoter activity. Expression of ICER from a r ecombinant adenoviral vector induced reactivation and decreased the percent age of LAT-positive neurons in neuronal cultures harboring latent HSV-1. Th ese results indicate that ICER represses LAT expression and induces reactiv ation of latent HSV-1.